Baseline tumour burden and prognosis in breast cancer treated with immune checkpoint inhibitors.

BackgroundImmune checkpoint inhibitors (ICI), alone or in combination with other agents, are now standard of care for a range of tumour types, including breast cancer. Radiological assessment of baseline tumour burden has been associated with prognosis in a variety of tumour types treated with immunotherapeutic agents. Whether baseline tumour burden is prognostic in breast cancer treated with ICI is unknown.MethodsA retrospective review of patients from a single institution with advanced breast cancer treated with ICI was performed. The sum of baseline target lesion measurements (baseline tumour size [BTS]) and all lesions (total tumour burden [TTB]) were determined in accordance with RECIST version 1.1 and correlated with clinical outcomes.Results82 patients were identified, treated between 2015 and 2020. BTS and TTB by quartile were significantly associated with overall survival (OS) (p